Conventional rotary mining tools generally comprise a lug or holder, mounted upon a rotary device or chain-like device, having a socket to receive a removable bit. The bit normally consists of shank portion for fitting within the lug socket, and a head portion provided with a hard, metal tip for cutting.
In some of such devices, the shank is mounted within the socket in such a way that the shank may rotate during operation of the tool for rotation of the tip point of contact with the rock, against which the tool is applied, to prevent excessive wear at any one point on the tip. However, in such cases, unless the bit shanks are kept constantly lubricated, small particles, such as dust and the like, tend to enter between the bit shank and the socket and ultimately jam one against the other to prevent further rotation. Thus, various configurations of bit and lug sockets and various methods have been tried to seal out the entry of dust or small particles.
Where the tool is used for drilling or cutting in areas in which there is considerable sand or sand-like particles, invariably, these particles work their way in between the shank and lug socket where they act as an abrasive to wear the surfaces of each and thereby shorten the bit life as well as the lug life and, at times, where they act to jam the shank against rotation. Thus, typically, where such type of cutters are used in sand or sand-like particle places, the bit life is substantially shortened due to excessive wear caused by such particles at the shank and also excessive wear upon small portions of the cutting tip due to inability to rotate the tip.
Thus, the invention herein relates to an improvement in such type of so-called rough cutter bits particularly useful in sand or sand-like particle areas. The purpose of this invention is essentially to reduce wear and/or jamming of the bit shank within the lug or holder by an approach which is the opposite to that normally followed, namely, by letting the particles freely pass through and around the shank and bore or socket, rather than trying to keep them out, as is conventional.